375 lines
9.8 KiB
Groff
375 lines
9.8 KiB
Groff
.\" $NetBSD: malloc.9,v 1.34 2003/07/16 12:04:26 wiz Exp $
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.\"
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.\" Copyright (c) 1996, 2003 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Paul Kranenburg, and by Jason R. Thorpe.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the NetBSD
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.\" Foundation, Inc. and its contributors.
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.\" 4. Neither the name of The NetBSD Foundation nor the names of its
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.\" contributors may be used to endorse or promote products derived
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.\" from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd July 16, 2003
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.Dt MALLOC 9
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.Os
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.Sh NAME
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.Nm malloc ,
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.Nm MALLOC ,
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.Nm realloc ,
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.Nm free ,
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.Nm FREE ,
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.Nm malloc_roundup ,
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.Nm malloc_type_attach ,
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.Nm malloc_type_detach ,
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.Nm malloc_type_setlimit ,
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.Nm MALLOC_DEFINE_LIMIT ,
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.Nm MALLOC_DEFINE ,
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.Nm MALLOC_DECLARE
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.Nd general-purpose kernel memory allocator
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.Sh SYNOPSIS
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.In sys/malloc.h
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.Ft void *
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.Fn malloc "unsigned long size" "struct malloc_type *type" "int flags"
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.Fn MALLOC "space" "cast" "unsigned long size" "struct malloc_type *type" \
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"int flags"
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.Ft void *
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.Fn realloc "void *addr" "unsigned long newsize" "struct malloc_type *type" \
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"int flags"
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.Ft void
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.Fn free "void *addr" "struct malloc_type *type"
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.Fn FREE "void *addr" "struct malloc_type *type"
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.Ft unsigned long
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.Fn malloc_roundup "unsigned long size"
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.Ft void
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.Fn malloc_type_attach "struct malloc_type *type"
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.Ft void
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.Fn malloc_type_detach "struct malloc_type *type"
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.Ft void
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.Fn malloc_type_setlimit "struct malloc_type *type" "unsigned long limit"
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.In sys/mallocvar.h
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.Fn MALLOC_DEFINE_LIMIT "type" "shortdesc" "longdesc" "limit"
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.Fn MALLOC_DEFINE "type" "shortdesc" "longdesc"
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.Fn MALLOC_DECLARE "type"
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.Sh DESCRIPTION
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The
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.Fn malloc
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function allocates uninitialized memory in kernel address space for an
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object whose size is specified by
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.Fa size .
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.Fn malloc_roundup
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returns the actual size of the allocation unit for the given value.
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.Fn free
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releases memory at address
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.Fa addr
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that was previously allocated by
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.Fn malloc
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for re-use.
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.Pp
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The
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.Fn realloc
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function changes the size of the previously allocated memory referenced
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by
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.Fa addr
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to
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.Fa size
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and returns a pointer to the
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.Pq possibly moved
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object.
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The memory contents are unchanged up to the lesser of the new
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and old sizes.
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If the new size is larger, the newly allocated memory is
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uninitialized.
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If the requested memory cannot be allocated,
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.Dv NULL
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is returned and the memory referenced by
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.Fa addr
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is unchanged.
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If
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.Fa addr
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is
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.Dv NULL ,
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then
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.Fn realloc
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behaves exactly as
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.Fn malloc .
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If the new size is 0, then
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.Fn realloc
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behaves exactly as
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.Fn free .
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.Pp
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The
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.Fn MALLOC
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macro variant is functionally equivalent to
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.Bd -literal -offset indent
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(space) = (cast)malloc((u_long)(size), type, flags)
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.Ed
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.Pp
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and the
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.Fn FREE
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macro variant is equivalent to
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.Bd -literal -offset indent
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free((caddr_t)(addr), type)
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.Ed
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.Pp
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The
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.Fn MALLOC
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macro is intended to be used with a compile-time constant
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.Fa size
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so that the compiler can do constant folding.
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In the comparison to
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.Fn malloc
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and
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.Fn free
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functions, the
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.Fn MALLOC
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and
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.Fn FREE
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macros may be faster, at the cost of increased code size.
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There is no difference between the memory allocated with MALLOC and malloc.
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i.e., no matter which MALLOC or malloc is used to allocate the memory,
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either FREE or free can be used to free it.
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.Pp
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Unlike its standard C library counterpart
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.Pq Xr malloc 3 ,
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the kernel version takes two more arguments.
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.Pp
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The
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.Fa flags
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argument further qualifies
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.Fn malloc
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operational characteristics as follows:
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.Bl -tag -offset indent -width M_CANFAIL
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.It Dv M_NOWAIT
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Causes
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.Fn malloc
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to return
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.Dv NULL
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if the request cannot be immediately fulfilled due to resource shortage.
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If this flag is not set
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(see
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.Dv M_WAITOK ) ,
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.Fn malloc
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will never return
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.Dv NULL .
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.It Dv M_WAITOK
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By default,
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.Fn malloc
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may call
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.Xr tsleep 9
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to wait for resources to be released by other processes, and this
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flag represents this behaviour.
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Note that
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.Dv M_WAITOK
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is conveniently defined to be 0, and hence may be or'ed into the
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.Fa flags
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argument to indicate that it's ok to wait for resources.
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.It Dv M_ZERO
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Causes the allocated memory to be set to all zeros.
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.It Dv M_CANFAIL
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Changes behaviour for
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.Dv M_WAITOK
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case - if the requested memory size is bigger than
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.Fn malloc
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can ever allocate, return failure, rather than calling
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.Xr panic 9 .
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This is different to M_NOWAIT, since
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the call can still wait for resources.
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.Pp
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Rather than depending on
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.Dv M_CANFAIL ,
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kernel code should do proper bound checking itself.
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This flag should only be used in cases where this is not feasible.
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Since it can hide real kernel bugs, its usage is
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.Em strongly discouraged .
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.El
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.Pp
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The
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.Fa type
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argument describes the subsystem and/or use within a subsystem for which
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the allocated memory was needed, and is commonly used to maintain statistics
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about kernel memory usage and, optionally, enforce limits on this usage for
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certain memory types.
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.Pp
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In addition to some built-in generic types defined by the kernel
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memory allocator, subsystems may define their own types.
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.Pp
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The
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.Fn MALLOC_DEFINE_LIMIT
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macro defines a malloc type named
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.Fa type
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with the short description
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.Fa shortdesc ,
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which must be a constant string; this description will be used for
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kernel memory statistics reporting.
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The
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.Fa longdesc
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argument, also a constant string, is intended as way to place a
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comment in the actual type definition, and is not currently stored
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in the type structure.
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The
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.Fa limit
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argument specifies the maximum amount of memory, in bytes, that this
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malloc type can consume.
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.Pp
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The
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.Fn MALLOC_DEFINE
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macro is equivalent to the
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.Fn MALLOC_DEFINE_LIMIT
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macro with a
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.Fa limit
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argument of 0.
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If kernel memory statistics are being gathered, the system will
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choose a reasonable default limit for the malloc type.
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.Pp
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The
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.Fn MALLOC_DECLARE
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macro is intended for use in header files which are included by
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code which needs to use the malloc type, providing the necessary
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extern declaration.
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.Pp
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Code which includes
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\*[Lt]sys/malloc.h\*[Gt]
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does not need to include
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\*[Lt]sys/mallocvar.h\*[Gt]
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to get these macro definitions.
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The
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\*[Lt]sys/mallocvar.h\*[Gt]
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header file is intended for other header files which need to use the
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.Fn MALLOC_DECLARE
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macro.
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.Pp
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The
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.Fn malloc_type_attach
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function attaches the malloc type
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.Fa type
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to the kernel memory allocator.
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This is intended for use by LKMs; malloc types included in modules
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statically-linked into the kernel are automatically registered with
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the kernel memory allocator.
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.Pp
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The
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.Fn malloc_type_detach
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function detaches the malloc type
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.Fa type
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previously attached with
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.Fn malloc_type_attach .
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.Pp
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The
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.Fn malloc_type_setlimit
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function sets the memory limit of the malloc type
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.Fa type
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to
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.Fa limit
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bytes.
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The type must already be registered with the kernel memory allocator.
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.Pp
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The following generic malloc types are currently defined:
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.Pp
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.Bl -tag -offset indent -width XXXXXXXXXXXXXX -compact
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.It Dv M_DEVBUF
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Device driver memory.
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.It Dv M_DMAMAP
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.Xr bus_dma 9
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structures.
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.It Dv M_FREE
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Should be on free list.
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.It Dv M_PCB
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Protocol control block.
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.It Dv M_SOFTINTR
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Softinterrupt structures.
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.It Dv M_TEMP
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Misc temporary data buffers.
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.El
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.Pp
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Other malloc types are defined by the corresponding subsystem; see the
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documentation for that subsystem for information its available malloc
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types.
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.Pp
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Statistics based on the
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.Fa type
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argument are maintained only if the kernel option
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.Dv KMEMSTATS
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is used when compiling the kernel
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.Po
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the default in current
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.Nx
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kernels
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.Pc
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and can be examined by using
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.Sq vmstat -m .
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.Sh RETURN VALUES
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.Fn malloc
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returns a kernel virtual address that is suitably aligned for storage of
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any type of object.
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.Sh DIAGNOSTICS
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A kernel compiled with the
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.Dv DIAGNOSTIC
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configuration option attempts to detect memory corruption caused by
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such things as writing outside the allocated area and imbalanced calls to the
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.Fn malloc
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and
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.Fn free
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functions.
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Failing consistency checks will cause a panic or a system console message:
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.Bl -bullet -offset indent -compact
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.Pp
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.It
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panic:
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.Dq malloc - bogus type
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.It
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panic:
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.Dq malloc: out of space in kmem_map
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.It
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panic:
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.Dq malloc: allocation too large
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.It
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panic:
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.Dq malloc: wrong bucket
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.It
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panic:
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.Dq malloc: lost data
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.It
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panic:
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.Dq free: unaligned addr
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.It
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panic:
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.Dq free: duplicated free
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.It
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panic:
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.Dq free: multiple frees
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.It
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panic:
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.Dq init: minbucket too small/struct freelist too big
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.It
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.Dq multiply freed item Aq addr
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.It
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.Dq Data modified on freelist: Aq data object description
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.El
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.Sh SEE ALSO
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.Xr vmstat 1
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